The Saturn IB was an upgraded and lightened version of the Saturn I, which was the first manned launch vehicle that was not directly derived from an ICBM. Designed early on as a part of the abandoned Earth Orbit Rendezvous method of reaching the moon, it was eventually developed as a manned launcher and used to qualify the Apollo Spacecraft for manned missions and for testing concepts used on the Saturn V such as clustering rocket engines. Later it would see use as the launcher for Skylab and the Apollo Soyuz Test Project astronauts. There were 19 Saturn I / IB launches. All were successful.